Nick,
Please feel very free to criticise these thoughts - I am extremely interested in both your facts and opinions on this subject:
"The S-76B tail rotor consumes 50 Hp while it hovers at 1050 Hp total power from the engines."
In cruise the vertical stabiliser takes over from tail rotor for anti-torque. Tail rotor loss becomes vertical stabiliser trim drag, but total anti-torque power requirement stays at the same 5%. Result is main rotor power requirement goes up, but tail rotor power will go down to 1%. Additionally in cruise main rotor hub presents a worse aerodynamic profile, unless the horizontal stabilisers produce more trim drag to keep same attitude.
The way i think about synchropters is that the tail rotor "migrates" up to where the main rotor is. The individual hub drag stays about the same, although there will be some adverse interference effects. In hover the synchropter beats conventional for power/weight requirement (better inflow to wake contraction and no swirl), although intermeshing complexity increases rotor mass. During transition to cruise, the synchropter will begin to suffer with a higher power requirement than the conventional (twin rotor/hub interference). By introducing variable blade twist and feathered retreating blade, this disadvantage can be lessened. Again the conventional can have active blade twist, but reverse velocity utilisation never allows ideal downwash distribution (retreating blade zero velocity circle).
The real decider comes when the conventional suffers retreating tip stall, at say >200 kts. If the intermesher is operating in outboard advancing ABC mode, this will start to beat the conventional for total power requirement since conventional can only use forward and rear rotor quadrants for lift. Eventually compressibility will limit top speed, but reduced synchropter rotor rpm will help attain a higher speed. Coaxial ABC is another alternative to the same ends, but will suffer far worse drag since hub fairing is virtually impossible.
Control is, agreed, not an issue. It is very easy by use of either gyro, large stabilisers or servo control to make either helicopter handle well (at a reasonable level of cost and reliability). For this reason breastroke rotation synchropters have, at best, a limited future.
Practical upshot: Only consider intermeshing for speeds > 200 kts.
Does this sound about right, or am i missing the plot somehow?
Mart
[Edit: to make point more clearly - and resolve headache
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